The invention relates to improvements in a mechanism for the comminution and grinding of brittle grinding stock such as cement clinker, or, coal or the like with equipment including a high pressure roll press, a tube mill, a deagglomeration chamber and at least one separator with the mechanisms operated and connected in an improved operational manner to reduce the energy consumption and improve the grinding and comminution abilities.
Efforts have been made to increase the very low energy utilization in comminution machines, particularly in tube mills or ball mills. For example, a two-stage facility for the comminution and grinding of brittle stock such as cement clinker that has not been pre-comminuted is known in EP Patent Application No. 0 084 383 wherein the grinding stock is first pressed under relatively high pressures in a first stage in the nip of a two-roll press leading in part to particle destruction and in part to the creation of incipient cracks in the particle interior. This results in the formation of agglomerates which are then deagglomerated in a second stage in a tube mill or ball mill with a comparatively low energy outlay and are then ground to finished product fineness.
The roll press is operated with a high pressing power, and more particularly, using more than 2 t/cm of roller length which produces agglomerates or scabs in the materials, the grindability of which is considerably improved in comparison to unpressed material so that the two-stage comminution leads to a noticeable reduction of energy requirement. As a consequence of the high pressing power of the roll press, for example, when pressing cement clinker granules, the agglomerates that are formed comprise a relatively high proportion of particles which have been already reduced to the desired cement fineness which is about 30% smaller than 90 .mu.m. These portions need not be further comminuted, but load the tube mill in the finished grinding of the agglomerates which is being done.
It is an object of the invention to utilize the concept of two-stage comminution and grinding but to modify the procedure and apparatus without the substantial outlay of additional apparatus expense and to obtain a saving in the specific energy requirements by relieving the tube mill of having to again process the discharged material of the roll press which has been already ground to the desired fineness of the finished product.
A further object of the invention is to provide means for deagglomerating the materials which are discharged from the roll press in a two-stage mechanism of the type described with the deagglomeration aiding in operation of the ball mill, increasing its capacity, and overall obtaining a uniform well comminuted material with a minimum of energy expenditure.
In accordance with the principles of the invention, the discharge material of the roll press is not supplied directly to the tube mill before or after deagglomeration. The material from the roll press is first supplied to a separator which may be a sifter or a cyclone type separator which separates the existing portion of the material out of the deagglomerated material which has already been ground fine enough to be complete. Only the coarse materials, that is, the grits of the separator are directed to the tube mill which is filled with the grinding bodies. The coarse material may be passed directly from the first separator to the tube mill or may be passed to a second separator which further separates completely fine material. For deagglomeration or breaking up of the discharged material from the roll press, there is provided a deagglomeration drum which receives the material and tumbles it to break it up. The deagglomeration drum co-rotates with the tube mill and is in communication with and located at the materials outlet of the tube mill. The materials inlet for the deagglomeration drum is in communication with the discharge of the roll press and the materials outlet of the deagglomeration drum communicates with the separator.
In accordance with the invention, the two stage comminution and grinding includes a rotary tube having two chambers in communication with each other with the one chamber having no grinding bodies therein and providing the deagglomeration chamber. The other chamber essentially operates as a ball mill and has grinding bodies therein forming the tube mill. The materials discharge conduit of the high pressure roll mill discharges into the end face of the rotary tube of the deagglomeration drum and the material as it breaks up, is passed to the separator. The separator then separates out the material which has been ground to a fineness meeting the standard required and passes it to a container for completed ground material, and the more coarse material is then passed to the tube mill. The tube mill conveniently discharges directly into the deagglomeration drum and the ground material passes up to the separator. Because the material which has been reduced to sufficient fineness in the roll press is separated, it does not have to be passed through the ball mill, thus reducing the quantity of material having to be processed in the ball mill. This effects an appreciable reduction of power consumption of the rotary tube mill. It also increases the effectiveness of the tube mill inasmuch as it is supplied only with material which requires grinding.
As set forth, the material discharges of the deagglomeration mill and tube mill come together and are collected by a common materials fall out housing which is stationary and in a preferred form, surrounds the tube mill and deagglomeration drum. The construction of the housing is such that it has openings for the passage of the deagglomerated material and of the ground material and an airstream is provided passing from the tube mill. This airstream, in a preferred form, is utilized for carrying the fine material from the out fall housing to the separator. In some forms of material, the airstream may be utilized to carry the entire discharge of material, and in other forms, separation may be effected so that the airstream carries only the fine material and the heavier material is physically carried, such as by a bucket elevator.
In a preferred arrangement, the upper region of the materials out fall housing is connected to a sifter which may take the form of a gravity air separator. The fine grained fraction of the deagglomeration drum will be entrained in the airstream to be carried up to the separator. The out fall housing may have a conduit connected to the lower region to receive the more coarse material which is then carried by a bucket elevator to be carried to the separator. In this arrangement, the finer portions of material discharged from the deagglomeration mill are conveyed in a pneumatic fashion to the separator and the coarser materials are conveyed mechanically. The sifting or separation of the fine materials from the more coarse materials in the deagglomeration mill can be accomplished by a static sifter such as a gravity air separator which has no rotating parts or by a dynamic sifter such as a cyclone air separator.